Electrically Conductive Material

ABSTRACT

An electrically conductive material includes: a supersaturated solid solution of a polycrystalline copper alloy having a composition represented by the formula: Cu 100-x-y M x N y ; wherein x and y are atomic ratios; wherein 0&lt;x≦2.0 and 0≦y≦2.0; wherein M is selected from Ru, Re, Ho, and combinations thereof; and wherein the supersaturated solid solution includes M precipitates formed at grain boundaries of the polycrystalline copper alloy when y is equal to zero, and includes M precipitates and MN particles formed at the grain boundaries of the polycrystalline copper alloy when y is not zero.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority of Taiwanese application no. 096128658, filed on Aug. 3, 2007.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an electrically conductive material, more particularly to an electrically conductive material capable of being annealed under a relatively high temperature.

2. Description of the Related Art

Copper has replaced aluminum as an interconnecting material in a semiconductor device due to its excellent properties, such as electric conductivity, electromigration resistance, etc. However, due to the lack of stability in mechanical properties under high processing temperatures in semiconductor processes, copper or copper alloy can incur problems, such as adhesion, current leakage, and thermal diffusion of copper into a Si substrate to react with silicon to form a copper-silicon compound, which results in an increase in resistivity of the semiconductor device.

It is known in the art that addition of element (s) or compound(s), such as carbon, W (tungsten), or WN (tungsten nitride), into a polycrystalline copper or polycrystalline copper alloy through sputtering techniques can result in a grain-refined structure that can reduce thermal diffusion of copper into the Si substrate during annealing of the polycrystalline copper alloy for reducing residual stress which can lead to reduction of the resistivity of the polycrystalline copper alloy. However, such improvement is still insufficient, and the annealing temperature can reach only a temperature ranging from 400° C. to 530° C. for the conventional polycrystalline copper alloys.

SUMMARY OF THE INVENTION

Therefore, the object of the present invention is to provide an electrically conductive material that can overcome the aforesaid drawback associated with the prior art.

According to the present invention, an electrically conductive material includes: a supersaturated solid solution of a polycrystalline copper alloy having a composition represented by the formula: Cu_(100-x-y)M_(x)N_(y); wherein x and y are atomic ratios; wherein 0<x≦2.0 and 0≦y≦2.0; wherein M is selected from the group consisting of Ru, Re, Ho, and combinations thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments of this invention, with reference to the accompanying drawings, in which:

FIG. 1 is a graph showing resistivity/annealing temperature relation of a polycrystalline copper alloy of Examples 1-4 according to this invention and Comparative Example 1;

FIG. 2 is an x-ray diffraction (XRD) graph of Examples 1 and 2;

FIG. 3 is an x-ray diffraction (XRD) graph of Examples 3 and 4 and Comparative Example 1;

FIG. 4 is an x-ray diffraction (XRD) graph of Example 5 according to this invention and Comparative Example 1;

FIG. 5 a is a transmission electron microscope (TEM) image of Example 1 taken before annealing;

FIG. 5 b is a selected area electron diffraction (SAED) image of Example 1 taken before annealing;

FIG. 6 a is a transmission electron microscope (TEM) image of Example 1 taken after annealing at an annealing temperature of 580° C.;

FIG. 6 b is a transmission electron microscope (TEM) image of Example 1 taken after annealing at an annealing temperature of 580° C.;

FIG. 7 a is a transmission electron microscope (TEM) image of Example 2 taken before annealing;

FIG. 7 b is a selected area electron diffraction (SAED) image of Example 2 taken before annealing;

FIG. 7 c is a dark field TEM image of Example 2 taken before annealing;

FIG. 8 a is a transmission electron microscope (TEM) image of Example 2 taken after annealing at an annealing temperature of 680° C.

FIG. 8 b is a transmission electron microscope (TEM) image of Example 1 taken after annealing at an annealing temperature of 680° C.; and

FIG. 9 is a graph showing current density/electric field intensity relation of Examples 1 and 2 and Comparative Example 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiment of an electrically conductive material according to this invention includes: a supersaturated solid solution of a polycrystalline copper alloy having a composition represented by the formula:Cu_(100-x-y)M_(x)N_(y); wherein x and y are atomic ratios; wherein 0<x≦2.0 and 0≦y≦2.0; wherein M is selected from the group consisting of Ru, Re, Ho, and combinations thereof.

In this embodiment, the supersaturated solid solution includes M precipitates formed at grain boundaries of the polycrystalline copper alloy when y is equal to zero, and includes M precipitates and MN particles formed at the grain boundaries of the polycrystalline copper alloy when y is not zero.

Preferably, the polycrystalline copper alloy is an annealed material that is annealed at a temperature ranging from 200° C. to 750° C.

Preferably, the polycrystalline copper alloy has a crystal grain size ranging from 30 nm to 150 nm.

It is noted that the annealing treatment is to eliminate the residual stress in the polycrystalline copper alloy so as to reduce resistivity of the polycrystalline copper alloy, and to provide energy for element M to precipitate from copper lattice sites and into the copper grain boundaries of the polycrystalline copper alloy, thereby preventing copper from diffusing into a Si substrate on which the polycrystalline copper alloy is formed.

In one embodiment, M is Ru, 0<x=≦2.0, and y=0, and the polycrystalline copper alloy, Cu_(100-x-y)Ru_(x), is preferably annealed at a temperature ranging from 300° C. to 580° C.

In another embodiment, M is Ru, 0<x≦2.0, and 0.01≦y≦2.0, and the polycrystalline copper alloy, Cu_(100-x-y)Ru_(x)N_(y), is preferably annealed at a temperature ranging from 300° C. to 680° C.

In yet another embodiment, M is Re, 0<x≦2.0, and y=0, and the polycrystalline copper alloy, Cu_(100-x-y)Re_(x), is preferably annealed at a temperature ranging from 300° C. to 560° C.

In still another embodiment, M is Re, 0<x≦2.0, and 0.01≦y≦2.0, and the polycrystalline copper alloy, Cu_(100-x-y)Re_(x)N_(y), is preferably annealed at a temperature ranging from 300° C. to 730° C.

In a further embodiment, M is Ho, 0<x≦2.0, and 0.01≦y≦2.0, and the polycrystalline copper alloy, Cu_(100-x-y)Re_(x)N_(y), is preferably annealed at a temperature ranging from 300° C. to 660° C.

The merits of the electrically conductive material of this invention will become apparent with reference to the following Examples and Comparative Example.

EXAMPLES Example 1 (E1)

A Si substrate was placed inside a magnetron sputtering system. A feed gas including argon plasma was introduced into the sputtering system under a working pressure of 1×10⁻² torr. After applying an output power of 150 W on a Cu—Ru target, a Cu_(100-x)Ru_(x) film, x=0.6, was formed on the Si substrate and had a thickness of approximately 300 nm. The sputtering operation was conducted at a sputtering rate of 4.8 nm/min. The temperature of the Si substrate was approximately 80° C. during the deposition of the Cu_(100-x)Ru_(x) film. Subsequently, specimens of the Cu_(100-x)Ru_(x) film thus formed were subjected to annealing treatment so as to eliminate residual stress therein and so as to enable Ru to precipitate from copper lattice sites and into copper grain boundaries. The annealing temperatures for the corresponding specimens were 200° C., 400° C., 580° C. and 600° C., respectively (see FIG. 1). A Pt film was then formed on each specimen of the Cu_(100-x)Ru_(x) film for microscope measurement.

Example 2 (E2)

The polycrystalline copper alloy of Example 2 was prepared using steps similar to those of Example 1, except that the feed gas included argon and nitrogen plasma. The polycrystalline copper alloy thus formed was Cu_(100-x-y)Ru_(x)N_(y), wherein x=0.4, and y=1.7. Subsequently, specimens of the Cu_(100-x-y)Ru_(x)N_(y) film thus formed were subjected to annealing treatment. The annealing temperatures for the corresponding specimens were 200° C., 400° C., 680° C. and 700° C. respectively (see FIG. 1).

Example 3 (E3)

The polycrystalline copper alloy of Example 3 was prepared using steps similar to those of Example 1, except that the target employed in the sputtering system was Cu—Re. The polycrystalline copper alloy thus formed was Cu_(100-x)Re_(x), wherein x=0.9. Subsequently, specimens of the Cu_(100-x)Re_(x) film thus formed were subjected to annealing treatment. The annealing temperatures for the corresponding specimens were 200° C., 400° C., 560° C. and 580° C., respectively (see FIG. 1).

Example 4 (E4)

The polycrystalline copper alloy of Example 4 was prepared using steps similar to those of Example 3, except that the feed gas included argon and nitrogen plasma. The polycrystalline copper alloy thus formed was Cu_(100-x-y)Re_(x)N_(y), wherein x=0.7, and y=0.06. Subsequently, specimens of the Cu_(100-x-y)Re_(x)N_(y) film thus formed were subjected to annealing treatment. The annealing temperatures for the corresponding specimens were 200° C., 400° C., 730° C. and 750° C. respectively (see FIG. 1).

Example 5 (E5)

The polycrystalline copper alloy of Example 5 was prepared using steps similar to those of Example 1, except that the target employed in the sputtering system was Cu—Ho, and the feed gas included argon and nitrogen plasma. The polycrystalline copper alloy thus formed was Cu_(100-x-y)Ho_(x)N_(y), wherein x=0.1, and y=0.09. Subsequently, specimens of the Cu_(100-x-y)Ho_(x)N_(y) film thus formed were subjected to an annealing treatment. The annealing temperatures for the corresponding specimens were 660° C. and 680° C., respectively.

Comparative Example 1 (CE1)

The polycrystalline copper alloy of Comparative Example 1 was prepared using steps similar to those of Example 1, except that the target was solely Cu. Subsequently, specimens of the Cu film thus formed were subjected to annealing treatment. The annealing temperatures for the corresponding specimens were 200° C., 300° C., 400° C., and 560° C., respectively (see FIG. 1).

FIG. 1 is a graph showing resistivity/annealing temperature relation of Examples 1-4 and Comparative Example 1. The results show that the resistivities of Examples 1-4 and Comparative Example 1 sharply increased under annealing temperatures of 600° C., 700° C., 580° C., 750° C., and 300° C., respectively. The resistivities of the polycrystalline copper alloy of Examples 1-4 remained stable under annealing temperatures of 580° C., 680° C., 560° C., 730° C. respectively.

FIG. 2 is an x-ray diffraction (XRD) graph of Examples 1 and 2, and shows that copper-silicon compound (Cu₃Si peak) was present under annealing temperatures of 600° C. and 700° C., respectively, while no Cu₃Si peak was found under annealing temperatures of 580° C. and 680° C., respectively. Hence, the resistivities of the polycrystalline copper alloy of Examples 1 and 2 can remain stable under annealing temperatures of 580° C. and 680° C., respectively.

FIG. 3 is an x-ray diffraction (XRD) graph of Examples 3 and 4 and Comparative Example 1, and shows that copper-silicon compound (Cu₃Si) was present in Example 3 and Comparative Example 1 under annealing temperatures of 580° C. and 400° C., respectively, and was absent in Examples 3 and 4 under annealing temperatures of 560° C. and 730° C., respectively. Therefore, the resistivities of the polycrystalline copper alloy of Examples 3 and 4 can remain stable under annealing temperatures of 560° C. and 730° C., respectively.

FIG. 4 is an x-ray diffraction (XRD) graph of Example 5 and Comparative Example 1, and shows that copper-silicon compound (Cu₃Si) was present in Example 5 and Comparative Example 1 under annealing temperatures of 680° C. and 400° C., respectively, and was absent in Example 5 under an annealing temperature of 660° C. Therefore, the resistivity of the polycrystalline copper alloy of Example 5 can remain stable under an annealing temperature of 660° C.

FIG. 5 a is a transmission electron microscope (TEM) image showing the morphology of Example 1. The copper crystal grain size of the polycrystalline copper alloy of Example 1 is about 8 nm-12 nm, which is an indication of the effectiveness of copper grain refinement attributed to the presence of Ru in the polycrystalline copper alloy before the annealing treatment.

FIG. 5 b is a selected area electron diffraction (SAED) image showing that the copper of the polycrystalline copper alloy has a crystal structure of face-centered cubic (FCC), which is an indication that Ru is in a supersaturated state in the copper lattice sites.

FIG. 6 a is a TEM image showing the morphology of Example 1 after the annealing treatment under a temperature of 580° C. The copper crystal grain size of the polycrystalline copper alloy is about 70 nm-75 nm, which is an indication that the presence of Ru restrains copper from re-crystallizing and refines the grain size, which prevents copper from diffusing into the Si substrate to react with silicon to form the copper-silicon compound.

FIG. 6 b shows only a native oxide layer was formed at an interface between the silicon substrate and the polycrystalline copper alloy film, which is an indication of absence of the copper-silicon compound.

FIG. 7 a is a transmission electron microscope (TEM) image showing the morphology of Example 2. The copper crystal grain size of the polycrystalline copper alloy is about 5 nm-10 nm, which is an indication of the effectiveness of copper grain refinement attributed to the presence of trace Ru and RuN_(z) in the polycrystalline copper alloy before the annealing treatment.

FIG. 7 b is a selected area electron diffraction (SAED) image showing that the copper of the polycrystalline copper alloy has a crystal structure of face-centered cubic (FCC). Moreover, the presence of RuN_(z) is an indication that Ru is in a supersaturated state in the copper lattice sites. A dark field TEM image (see FIG. 7 c) shows that the RuN_(z) crystal grain size is approximately 4 nm.

FIG. 8 a is a TEM image showing the morphology of Example 2 after the annealing treatment under a temperature of 68° C. The copper crystal grain size of the polycrystalline copper alloy is about 90 nm-95 nm, which is an indication that the presence of Ru restrains copper from re-crystallizing and thus refines the copper grain size, which prevents copper from diffusing into the Si substrate to react with silicon to form copper-silicon compound.

FIG. 8 b shows only a native oxide layer was formed at an interface between the silicon substrate and the polycrystalline copper alloy film, which is an indication of absence of the copper-silicon compound.

FIG. 9 is a graph showing current density/electric field intensity relation of Examples land 2 and Comparative Example 1. The current densities of Comparative Example 1 and Examples 1 and 2 are 10⁻⁷, 10⁻⁸ and 10⁻⁹ (A/cm²), respectively, under an annealing temperature of 400° C.

Specimens of each of Comparative Example 1 and Examples 1 and 2 were subjected to adhesion tests after annealing at different annealing temperatures of 200° C. and 300° C.

Table 1 shows the adhesion tests for Comparative Example 1 and Examples 1 and 2 based on the standard of ASTM-D3359-B.

TABLE 1 Annealing Composition temperature(° C.) Adhesion CE1 Cu none 0 200 0 300 0 E1 Cu_(100−x)Ru_(x) none 4 200 4-5 300 4-5 E2 Cu_(100−x−y)Ru_(x)N_(y) none 5 200 5 300 5

The results show that the polycrystalline copper alloy of this invention has an excellent adhesion to the silicon substrate.

It has thus been shown that, by adding the material such as Re, Ru Ho, and combinations thereof into polycrystalline copper, the aforesaid drawback associated with the prior art can be eliminated.

With the invention thus explained, it is apparent that various modifications and variations can be made without departing from the spirit of the present invention. It is therefore intended that the invention be limited only as recited in the appended claims. 

1. An electrically conductive material comprising: a supersaturated solid solution of a polycrystalline copper alloy having a composition represented by the formula: Cu_(100-x-y)M_(x)N_(y); wherein x and y are atomic ratios; wherein 0<x≦2.0 and 0≦y≦2.0; wherein M is selected from the group consisting of Ru, Re, Ho, and combinations thereof.
 2. The electrically conductive material of claim 1, wherein said supersaturated solid solution includes M precipitates formed at grain boundaries of said polycrystalline copper alloy when y is equal to zero, and includes M precipitates and MN particles formed at the grain boundaries of said polycrystalline copper alloy when y is not zero.
 3. The electrically conductive material of claim 1, wherein said polycrystalline copper alloy is an annealed material that is annealed at a temperature ranging from 200° C. to 750° C.
 4. The electrically conductive material of claim 1, wherein said polycrystalline copper alloy has a crystal grain size ranging from 30 nm to 150 nm.
 5. The electrically conductive material of claim 1, wherein M is Ru, 0<x≦2.0, and y=0.
 6. The electrically conductive material of claim 5, wherein said polycrystalline copper alloy is an annealed material that is annealed at a temperature ranging from 300° C. to 580° C.
 7. The electrically conductive material of claim 1, wherein M is Ru, 0<x≦2.0, and 0.01≦y≦2.0.
 8. The electrically conductive material of claim 7, wherein said polycrystalline copper alloy is an annealed material that is annealed at a temperature ranging from 300° C. to 680° C.
 9. The electrically conductive material of claim 1, wherein M is Re, 0<x≦2.0, and y=0.
 10. The electrically conductive material of claim 9, wherein said polycrystalline copper alloy is an annealed material that is annealed at a temperature ranging from 300° C. to 560° C.
 11. The electrically conductive material of claim 1, wherein M is Re, 0<x≦2.0, and 0.01≦y≦2.0.
 12. The electrically conductive material of claim 11, wherein said polycrystalline copper alloy is an annealed material that is annealed at a temperature ranging from 300° C. to 730° C.
 13. The electrically conductive material of claim 1, wherein M is Ho, 0<x≦2.0, and 0.01≦y≦2.0.
 14. The electrically conductive material of claim 13, wherein said polycrystalline copper alloy is an annealed material that is annealed at a temperature ranging from 300° C. to 660° C. 